Rolling method and apparatus



March 1967 1.. F. COFFIN, JR 3,309,968

ROLLING METHOD AND APPARATUS Filed Sept. 28, 1964 lnvenfor: Louis E C0ff/h,./r.,

United States Patent 0 3,399,998 RGLLING METHQD AND APPARATUS Louis F. Cofiin, 312, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Sept. 28, 1964, Ser. No. 399,549 5 Claims. (Cl. 72213) The present invention relates generally to the art of shaping and forming materials such as metals and is more particularly concerned with novel method and apparat us for changing the cross-sectional dimensions and increasing the length of a portion of an elongated body while the body is being rolled in accordance With the unique process disclosed and claimed in my US. Patent 3,238,756, issued Mar. 8, 1966, and assigned to the present assignee.

This invention is predicated upon my discovery that edge-cracking tendencies in sheet, strip and foil rolling in accordance with my prior invention disclosed and claimed in the aforesaid patent can be effectively eliminated by reducing the thickness of the edge portions of sheet, strip or foil stock at a rate greater than the rate of reduction of the stock central portion. This invention is further predicated upon my discovery that as a practical matter, this differential reduction or thinning rate can readily be established and maintained through the application to the edge portions of the stock of compression forces of greater magnitude than the compression forces applied to the stock central portions. Thus, in effect, in accordance with this invention it is possible substantially to equalize the distribution of tensile forces across th width of the stock and even to reverse the usual condition and have greater tensile forces in the stock central portion than in its edges. In other words, compression or rolling forces are distributed across the width of the stock in such a way as to produce in combination with the tensile forces greater reduction and elongation of the edge portions than of the central portion.

This invention is additionally based upon my discovery that it is possible to establish and maintain the normal compression force distribution required across the width of sheet, strip or foil stock in the course of a rolling op eration by plastically bending the stock around a floating bend roller and pulling the ends of the bend roller against support rolls and thereby elastically deflecting or bending the bend roller with the stock edge portions as fulcrums in this underbeam loading operation.

In its method aspect, this invention comprises the steps of cyclically plastically bending in sequence successive longitudinal portions of sheet, strip or foil stock and simultaneously subjecting the successive portions of the stock in the same sequence to tension stress and to compression forces sufiicient in combination with the tension stress and the plastic bending stresses to reduce the thickness of the stock and increase its length, the compression forces being distributed across the width of the stock so that the stock edge portions are subjected to greater compression forces at any given time than the central portion therebetween with the result that the strip edge portions of each successive longitudinal portion of the stock are reduced to a greater extent than the intervening or central portion.

In its apparatus aspect, this invention comprises two contact rolls together defining a gap or a saddle between them and a floating third roll disposed between the contact roll gap and having stock-engaging central portion and end portions. This apparatus also incorporates roll force regulating means engaging the third roll to move the third roll toward the narrowest part of the gap and thereby apply greater compressive forces to the edge portions than to the central portions of stock in process between 3,3fihfifi8 Patented Mar. 21, 1967 "ice the contact rolls and the third roll. In a preferred embodiment of this invention, the bend roll itself is bendable and a yoke is provided to connect the end portions of the bend roll to apparatus which through the yoke can be used to pull or push the bends of the bend roll toward the contact rolls with the stock therebetween and thus elastically deflect or bend the bend roll around the edges of the stock as fulcrums. In another preferred embodiment of the invention, the bend roll is contoured in modified hourglass form so that the edge portions of the stock are subject to greater compressive forces as the bend roller is pulled by the stock and elastically deflected with the stock edges as fulcrums.

With reference to th drawings accompanying and forming a part of this specification:

FIG. 1 is a fragmentary perspective view illustrating somewhat diagrammatically apparatus of this invention implementing in a preferred way the novel method of this invention;

FIG. 2 is a fragmentary perspective view of the FIG. 1 apparatus showing more completely the structural features of the invention and the manner in which the contact rolls are supported in fixed position and th manner in which the bend rollers is supported and moved relative to the contact olls to produce the results of this new invention method;

FIG. 3 is a diagrammatic view of the FIG. 2 apparatus;

FIG. 4 is a fragmentary sectional view of the FIG. 3 assembly taken on line 44 thereof but exaggerating the bending of the bend roll and incorporating a roll force diagram which indicates the distribution of aggregate compression force across the width of stock in the pass between one contact roll and the bend roll; and

FIG. 5 is a combination view like that of FIG. 4 of an alternative apparatus incorporating a bend roller of modified hourglass shape and showing again diagrammatically the distribution of total roll force applied across the full width of stock in a bend roll-contact roll pass.

As indicated above, the central novel concept of this invention is the reduction and elongation of the edge portions of the stock relative to the central portion thereof during he special novel rolling operation-s described in my aforesaid copending application. By thus in creasing the length of the edge portions of the stock, the tendency for tensile forces to build up to an extent where edge cracking will occur in such rolling operatic-ns is avoided. In accordance with this novel concept, the edge portions of the strip are subjected to a combination of deformation forces which are somewhat greater than the deformation forces applied to the portion of the stock between the edge portions and resulting in the greater reduction and elongation of those edge portions. The compression force applied to each edge portion is greater than the compression force applied to the central part of the stock but the tension stress in the central portion of the stock is greater than it is in the edge portions. Further, it is preferable that the total deformation forces applied to each edge portion of the stock are approximately the same so that the stock along each of its edges is elongated and reduced to about the' same extent and to a somewhat greater extent than the central portion. This kind of force distribution across the width of the stock can be accomplished in a variety of ways. The apparatus illustrated in the accompanying drawings represents two different preferred ways of accomplishing this result but other less practical equipment implementing the basic concept and leading to this desired result can be envisioned. Thus, for example, the stock may be fitted with thin strips along its edge portions to increase the efiective thickness of the stock edge portions and to correspondingly increase the compression force and the combined tension and compression forces in those regions relative to the central portion of the stock. In this instance, external bending of the bend roller or special contouring of it as shown in the drawings would not be essential to the desired result but the bend roll could, if desired, be supported in fixed position relative to the contact rolls. If the central portion reduction were not accomplished to the desired extent in one pass, the auxiliary edge portion strips could be removed for a second pass of the stock through the mill in order to bring the thickness of the central portion more closely to that of the edge portions.

As shown in FIG. l, sheet stock S is rolled in accordance with the present method by means of a mill comprising a pair of contact rolls and 11 of a relatively large diameter and a bend roller 12 of much smaller diameter. Contact rolls 1t) and 11 and bend roll 12 are disposed with their axes parallel, the contact rolls defining between them a gap or saddle at the entrance of which bend roller 12 is disposed. Stock S is disposed around contact roll 10 and is looped around bend roll 12 and then is taken out of the mill around contact roll 11. As the arrows indicate, the stock moves downwardly through the mill and is subjected to tension at all times and is subjected to tension-dependent compressive forces at points where the stock passes between contact rolls and the bend roller. Contact rolls 10 and 11 are driven in speed ratio to each other to maintain predetermined tensile stress in the stock as it is conveyed through the mill in non-slipping engagement with the contact rolls, roll 11 being driven faster than roll 10 to accommodate the elongation of the stock occurring at the points of reduction on each side of the bend roller. The bend roller, in turn, is an idler which,

as the arrows directed at its end portions indicate, is subjected to forces tending to move the bend roller toward the narrowest portion of the gap between the contact rolls, these forces being of magnitude sufiicient to cause the bend roller to bend, as will be described more in detail below, and thereby to apply maximum compression forces in the region of the edge portions of the stock 5 at the points where the stock is gripped between the bend roll and the respective contact rolls. Thus, tension created in the stock through the action of the driven contact rolls results in the bend roller being drawn firmly against the stock portions between the bend roller and the contact rolls, and the edge rolling compression forces are superimposed on the compression forces attributable to stock tension.

The apparatus of FIG. 2 is a specific embodiment of the general apparatus illustrated in FIG. 1 and thus comprises a pair of driven contact rolls 15 and 16 of the same diameter and the bend roll 17 of much smaller diameter disposed with its axis paraiiel to the axes of the contact rolls and in the saddle defined by those rolls. Contact rolls 15 and 16 are journalled in rolling-mill structure generally indicated at 2% and are driven by suitable drive means, such as a chain and sprockets assembly, in predetermined speed ratio to each other. Accordingly, an illustration of the drive means and further description thereof in this specification is unnecessary to a complete understanding of the present invention. Bend roll 17 is maintained in the saddle between contact rolls 15 and 16 by strip S which is threaded through the mill and cradles roll 17, benig disposed over roll 15 and under roll 17 and then over roll 16 and out of the mill, as the arrows indicate. Bend roll 17 is adjusted as to roll force or pressure distribution across the width of the strip by means of yoke 21, the lower ends of the two arms of which are provided with openings through which end portions of bend roll 17 are disposed as shown in FIG. 2. Thus, bend roll 17 is actually journaled in the yoke and is moved upwardly with the yoke by lifting means (not shown) connected to the yoke. Bend roll 17, as it is rotating in operation, is caused to exert against the stock in process predetermined compression force beyond that induced from stock tension and in doing so, to bend or deflect around the edges of the stock causing greater deformation in those regions than in the central portion thereof in accordance with the basic objective of the present invention concept. The apparatus for operating yoke 21 to accomplish this result may be any suitable lifting means such as a crane, from which the yoke is suspended in the usual manner. The lifting means thus works against the weight of the mill in accomplishing the bending of bend roll 17 and the nonuniform reduction and elongation of stock S.

In FIG. 3, the geometry of the FIG. 2 apparatus is more clearly illustrated and the effect of this geometry is further shown in FIGS. 4 and 5. Thus, as yoke 21 is drawn upwardly relative to mill frame 20 tending to carry bend roll 17 with it, the bend roll actually bends along its length and so compresses and thins the edge portions of the stock to a considerably greater extent than the central portion thereof. Actually, in FIG. 4 the bending effect and the resulting thinning of the stock edge portions is exaggerated for purposes of illustration. As force diagram A superimposed on the sectional view shows, however, the bend roll exerts some significant compressive force against stock S across its full width but maximum roll forces are applied to the stock edge portions as the stock tension-induced roll force is aug mented by the lifting or pulling force applied to the bend roll through yoke 21.

FIG. 5 illustrates the alternative form of apparatus described generally above wherein bend roll 25, by virtue of its longitudinal cross-sectional shape, again accomplishes the effect obtained in the FIG. 3 and FIG. 4 geometry by bending or elastically deflecting the bend roll. In this instance, however, the end portions of bend roll 25 are free and unsupported but as in the FIG, 4 assembly, stock S is gripped between the bend roll and a contact roll 25, preferably of somewhat larger diameter than the bend roll. By virtue of the shape of the bend roll, stock emerging from the mill of FIG. 5 will have a typical cross-sectional shape like that of stock emerging from the FIG. 3 and FIG. 4 apparatus. This result is attributable, again, to the distribution of compression or roll force across the width of the stock as shown in force diagram B superimposed on FIG. 5.

In the actual practice of this invention using commercial low-carbon steel cold-worked strip (full-hard black plate) and apparatus as described with reference to FIGS. 2, 3 and 4 above, I have accomplished heavy reductions in cold-rolling operations without the development of edge cracks in the stock. The strip was three inches wide and 4.9 mils thick and in two passes through the apparatus was reduced in thickness to 2.8 mils and then to 1.6 mils. Contact rolls 10 and 16 were six inches in diameter and bend roll 15 of hardened alloy tool steel was of uniform /3 inch diameter over its full length. A pulling force of pounds was applied to roll 12 through yoke 21 throughout each run of the strip through the apparatus. In operations of this kind, except that the bend roll is not elastically deflected by forces applied to its end portions and the compression force applied to the strip is not augmented in the edge portions of the strip, edge cracking leading to ultimate strip breakage is a common result.

In another similar rolling operation carried out on the same kind of strip material, contoured bend roll 25 was used as illustrated in FIG. 5. Roll 25 of hardened alloy tool steel was provided with a 1.5 mil diametral concavity over a length of four inches in its central portion and was of 0.446 inch diameter at its center. Rolls 15 and 16 were again of six inch diameter and regular cylindrical form. A 34 percent reduction in thickness was taken in the strip (from 4.9 mils to 3.2 mils) in one pass through the mill and a 41 percent reduction was taken in another length of the same strip in a similar run through the mill (from 4.9 mils to 3.0 mils). In each case, the strip was centered in the concavity of the bend roll and in each case the rolled strip was free from edge cracks in contrast to the usual experience in rolling this material in this apparatus and under generally the same conditions except for the lack of supplemental edge rolling force provided through the contoured bend roll.

It will be understood by those skilled in the art that in this specification and in the appended claims the terms compression forces and compressive forces are used in the usual manner to mean and refere to the roll forces applied to the stock surface rather than forces applied to the stock edges and transversely. The terms tension forces and tension stresses are similarly used in reference to those forces and stresses applied and developed longitudinally of the stock.

Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject matter which I regard as being my invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the specifically described embodiments of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for increasing the length and reducing the thickness of metal strip, sheet or foil stock which comprises two contact rolls together defining a gap or saddle, a floating third roll disposed between the two contact rolls and having a strip-engaging central portion and end portions, and third roll bending means engaging the third roll at two paints separated by the said central portion to move said end portions toward the two contact rolls.

2. Apparatus for increasing the length and reducing the thickness of metal strip, sheet or foil stock which comprises two relatively large diameter contact rolls on fixed centers and together defining a gap or saddle, a floating relatively small diameter third roll disposed be tween the two contact rolls and having a strip-engaging central portion and end portions, and roll force regulating means engaging the third roll end portions to move said end portions relative to the two contact rolls, said strip-engaging means including yoke means secured to the third roll and spanning the strip-engaging portion of said third roll,

3. Apparatus for increasing the length and uniformly reducing the thickness of metal strip, sheet or foil stock which comprises two contact rolls on fixed centers and together defining a gap or saddle, a floating third roll disposed between the two contact rolls with its axis substantially parallel to the axes of said contact rolls and having a strip-engaging central portion and end portions, and roll force regulating means spanning the said roll centrol portion and separately engaging the third roll end portions to pull said end portions simultaneously toward the two contact rolls.

4. Apparatus for increasing the length and uniformly reducing the thickness of metal strip, sheet or foil stock which comprises two relatively large diameter contact rolls on fixed centers and together defining a gap or saddle, a floating relatively small diameter bend roll disposed in the gap between the two contact rolls and having a stripengaging central portion and end portions extending outboard of the contact rolls, and roll force regulating means engaging the bend roll end portions to pull said end portions further into the gap between the contact rolls, said regulating means including a yoke straddling the contact rolls and secured to the bend roll end portions outboard of said contact rolls, and pulling means operatively connected to the yoke to move the bend roll toward and away from the narrowest portion of the contact roll gap.

5. in the method of rolling metal strip and reducing its thickness and increasing its length by cyclically plasticaily bending in sequence successive longitudinal portions of the strip and simultaneously subjecting the successive portions in the same sequence to tension stress, the combination of the step of simultaneously subjecting the strip across its width at each bend location to compression forces which are greater in the strip edge regions than in the strip central portion and thereby reducing the strip thickness to a greater extent in the edge portions than in the strip central portion.

References Cited by the Examiner UNITED STATES PATENTS 1,048,793 12/1912 Beeman et al. 72-234 2,291,361 7/1942 Walsh 72-205 2,332,796 10/1943 Hume 72-205 2,392,323 1/1946 Koss 72-205 CHARLES W. LANHAM, Primary Examiner.

H. D. HOINKES, Assistant Examiner. 

1. APPARATUS FOR INCREASING THE LENGTH AND REDUCING THE THICKNESS OF METAL STRIP, SHEET OR FOIL STOCK WHICH COMPRISES TWO CONTACT ROLLS TOGETHER DEFINING A GAP OR SADDLE, A FLOATING THIRD ROLL DISPOSED BETWEEN THE TWO CONTACT ROLLS AND HAVING A STRIP-ENGAGING CENTRAL PORTION AND END PORTIONS, AND THIRD ROLL BENDING MEANS ENGAGING THE THIRD ROLL AT TWO PAINTS SEPARATED BY THE SAID CENTRAL PORTION TO MOVE SAID END PORTIONS TOWARD THE TWO CONTACT ROLLS. 